Two Novel Designs Of Dual-Band Branch-Line Coupler

In recent years,with the development of wireless communication system,various commercial needs and military applications have more complicated requirements for communication equipment.In order to meet all kinds of requirements,microwave systems are developing in the direction of high integration,broadband,dual or multi-band,large frequency ratio.As an important part of microwave and millimeter wave system,the performance of coupler directly affects the whole performance of microwave system.There are many types of couplers,among which the branch-line coupler has the characteristics of simple structure and easy integration in processing.Therefore,the branch-line coupler has become a research hotspot.The coupler designed in this thesis is innovatively studied on the basis of dual-band coupler,so that the coupler has other functions to meet the needs of microwave system.The main research conclusions of this thesis can be summarized as follows:1.A dual-band and wide-band branch-line coupler with a large frequency ratio is proposed.Firstly,on the basis of dual-band cross-coupled coupler,the cascade technique is applied to enhance the bandwidth of each frequency band.Secondly,the frequency ratio range of the coupler is determined.When the coupler works at a large frequency ratio,the characteristic impedance value is too high to be processed easily.Therefore,the defect ground structure is applied to solve this problem.Finally,the measured results show that the relative bandwidth of the coupler at low frequency band and high frequency band is34.7%and 14.9%,respectively,and the frequency ratio of the coupler reaches 2.6.2.A miniaturized dual-band coupler with harmonic suppression is proposed.Firstly,the dual-band and harmonic suppression structure is applied to the branch-line coupler.Secondly,harmonic suppression of 5f₁ and 7f₁ is realized by adjusting the length of open shunt stub.Finally,optimization function is used to optimize the electrical length of the coupler to achieve miniaturization.The measured results show that the coupler can effectively suppress the harmonics of 5f₁ and 7f₁.The electrical length of the proposed coupler is 0.18?·0.22?,and the relative size of the coupler is 62.53%compared with the traditional branch-line coupler.